A. Field of the Invention
This invention relates to perpendicular magnetic recording media. More specifically, this invention relates to perpendicular magnetic recording media which is inexpensive and has excellent magnetic characteristics. This invention also relates to a perpendicular magnetic recording apparatus comprising such perpendicular magnetic recording media.
B. Description of the Related Art
Perpendicular magnetic recording media generally have a structure in which a substrate, backing layer, seed layer, intermediate layer, magnetic layer, and protective layer are deposited in order. Given such a structure, various research and development is being performed relating not only to the magnetic layer, but also to the intermediate layer positioned immediately below this magnetic layer, in order to improve the various characteristics desired of perpendicular magnetic recording media, such as the magnetic characteristics and the read/write characteristics.
For example, when using an alloy the principal component of which is Co as the magnetic layer, efforts are being made to use various materials in the intermediate layer in order to control the crystal orientation, crystal grain diameters, segregation structure, and similar of the magnetic layer. In representative cases, Ru or an alloy of Ru is used as the intermediate layer material, and the following technologies have been disclosed for such magnetic recording media.
In T. Oikawa, M. Nakamura, H. Uwazumi, T. Shimatsu, and H. Muraoka, members IEEE, and Y. Nakamura, fellow, IEEE: IEEE Transactions on Magnetics, Vol. 38, No. 5, September 2002, perpendicular magnetic recording media are disclosed in which a magnetic layer with SiO2 added to Co alloy (CoPtCr) is grown epitaxially on a Ru underlayer (intermediate layer).
In Japanese Patent Laid-open No. 2001-283428, perpendicular magnetic recording media are disclosed in which the magnetic film comprises an alloy, the main component of which is Co, and the intermediate layer is an alloy, the main components of which are Ru and a material having a body-centered cubic structure, which comprises 60 at % or higher Ru.
Thus in the technologies disclosed in the report of T. Oikawa et al. and in Japanese Patent Laid-open No. 2001-283428, Ru is used in the intermediate layer positioned directly below the magnetic layer (film). Ru is an extremely expensive material, but until now there has been almost no material appropriate for use in an intermediate layer, the magnetic characteristics of which have surpassed those of Ru or a Ru alloy. Hence the manufacturing cost of intermediate-layer materials in perpendicular magnetic recording media has been high.
Re is known as a substitute material for Ru in intermediate layers, but the cost of the intermediate-layer material also remains high when Re is used, and so there has been a need to develop technology for application of inexpensive materials in intermediate layers in place of Ru and Re.
In light of these circumstances, the following has been disclosed as specific technology for formation of an intermediate layer without using Ru or Re.
Japanese Patent Laid-open No. 2003-123245, corresponding to U.S. Pat. No. 6,682,826, discloses magnetic recording media, employing, as an orientation control film equivalent to an intermediate layer, Ge, Cu, Ni, Au, Pd, or similar, as substitutes in addition to cases in which Ru or Re is used, and in which the difference between Δθ50 for the intermediate layer and the magnetic layer is within a specified range (from 1 to 8 degrees). Formation of crystal grain boundaries in the initial magnetic layer growth period is promoted by means of this media, and magnetic characteristics can be improved.
However, when Ru or Re is not used in the intermediate layer, if the magnetic layer thickness is reduced in order to increase the recording density, orientation of the intermediate layer and magnetic layer declines as a result, and media noise is increased. Hence there has been a need to develop magnetic recording media for high-density recording which employs inexpensive materials yet exhibits magnetic characteristics comparable to or surpassing those achieved using Ru or Re.
As described above, various perpendicular magnetic recording media have been disclosed, but there remain demands for perpendicular magnetic recording media which exhibit excellent high-density recording and other magnetic characteristics, while employing an intermediate layer formed by inexpensive means. The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.